1. Field of the Invention
The present invention relates to a micro-geometry measuring device for precisely measuring surface geometry of LSI, semiconductor wafers, or the like.
2. Description of Related Art
Special devices are used for precisely measuring surface geometry of semiconductor wafers, etc. Published Japanese translation of PCT international publication for patent applications No. Hei 8-502357 and U.S. Pat. No. 5,309,755 are known as conventional examples of such device.
The conventional example has an arm rotatably supported by a frame through a flexural pivot (elastic hinge), an end of the arm having a stylus made of a diamond tip and the other end of the arm having a movable plate.
The movable vane (plate) moves between two parallel plates fixed to a base, the movable plate forming a bridge-electrode together with the parallel plates to be a pair of capacitor. When the arm pivotally moves, equilibrium of the bridge is lost and displacement of an end of the stylus is measured. Since the movable plate moves between the two parallel plates, the movable plate receives resistance of air and appropriate damping effect can be expected.
A lever arm is provided to a central portion of the arm. A tip provided at an end of the lever arm is controlled by a magnetic field of a biasing mechanism to keep a constant measuring force at a pointed end of a stylus. The control is conducted by feedback of displacement amount of stylus end.
Stabilization of the measuring force will be described below.
Without the feedback control by the biasing mechanism, since the arm is rotatably supported by the elastic hinge, the measuring force fluctuates in accordance with rotation angle of the arm as shown in solid line p in a graph of FIG. 7. In other words, the measuring force differs according to a position of the stylus or a magnitude of irregularity of a workpiece, which causes error in detection result of surface position of the workpiece, and, when angle fluctuation is large, the measuring force can be so excessive as to effect bad influence on the surface of the workpiece.
Accordingly, the biasing mechanism is provided to the lever arm and magnetic force is applied therefrom, thereby conducting correction corresponding to measuring force fluctuating in accordance with the angle. If the correction results in a characteristic shown in dotted line Q in the graph of FIG. 7, the measuring force can be largely reduced from f1 to f2 at the arm rotation angle shown by D in the graph.
Incidentally, for correcting measuring force by the biasing mechanism of the above-described conventional example, the displacement amount of the stylus end is detected, which is fed back to magnetic intensity at the distal end of the lever arm.
However, in the conventional example, the measuring force working onto the stylus and the workpiece is not directly detected for control, but the position of the movable plate is detected for indirect control based on the position value. On account of the indirect control, the measuring force cannot be controlled (stabilized) precisely enough for the stylus to accurately follow the irregularity on the surface of the workpiece.
On the other hand, the measuring force itself may be increased for the stylus to accurately follow the surface of the workpiece. However, micro-geometry on the workpiece surface is likely to be damaged by the stylus in the above arrangement.
Further, since the measuring force is controlled by the distal end of the lever arm, mechanical rigidity between the stylus and the distal end of the lever arm is small in the conventional example, so that responsivity thereof cannot be improved.
Accordingly, the measuring force working between the stylus and the workpiece is fifty microgram-force (.mu.gf) at the minimum, and measurement is difficult at a lower measuring force or with a faster arm movement.